Because mammalian placentas are plentiful and are normally discarded as medical waste, they represent a unique source of medically-useful cells, e.g., placental stem cells. When cultured/present in certain environments, e.g., in vivo, cells can exhibit decreased survival due to the presence of environmental factors that act as insults to the cells. There exists a need for populations of placental stem cells that are resistant to such insults, and thus survive for longer periods of time in environments that would normally cause cell survival to diminish.